Courtesy of Bob Dugan
You may have dissected a worm or frog (or if you were really lucky a pig!) in high
school, but have you ever looked into the guts of a computer? Most computer users treat
computer hardware and software as a mysterious black box. As a computer scientist,
however, part of your job will be to lift the veil of mystery and learn the inner workings
of computer hardware and the programs that use this hardware.
You should see a computer in front of you that looks like this:
It's an old computer.Got your dissecting gloves on? GOOD. Remove the cover release
screws and pull the
cover off like this:
NOW you are looking at the guts of the computer. The dissection you are about to
perform has some distinct advantages over your high school biology lab. Computer guts:
a) Do not smell like formaldehyde
b) Do not feel slimy
c) Do not bite
On the negative side, however, you don’t want to dissect a computer when the power is
on. Also computer parts can get dusty so you may need to wash your hands after class.
These hardware components can help you make better sense of the following schematic
of the computer. A schematic is the engineering equivalent of biology’s anatomical
Oops... that’s the frog. Ok here is the computer schematic:
Most of the labels are self explanatory. All of the hardware is connected the green board
you see here. The green board is called the “Motherboard”.
The I/O cards, however need some explanation. An I/O card is an input/output interface
between the computer and some external device. One card, for example, sends graphic
signals to the computer monitor and provides audio signals for computer speakers.
Another card connects the computer to the internet.
Remove the CPU from the computer and hold it in your hand...
Pretty big huh? Most of what you are looking at is called “packaging”. The physical
CPU is hidden deep inside and looks like a wafer thin piece of silicon. You can’t see this
wafer without taking a sledgehammer to the packaging:
Moore’s Law states that the distance between CPU components halves every 18 months.
Electrons have a shorter distance to move between components, which doubles the speed
of the CPU. Shortening this distance also means more components can fit on the CPU.
More components means there are more electrons flying around more wires between the
components. The downside of all this is that an electron generates heat as it moves
through a wire.
QUESTION: What is the purpose of those strange metal prongs attached to the CPU?
HINT: Look at how the CPU is placed on the motherboard with respect to some of the
components you classified as OTHER in a previous question. .
Back up for a second and look at that CPU. Remember that we were just talking about
Moore’s Law which states that the processing power of a CPU doubles every 18 months.
For now we’re going to measure the processing power of a CPU using a unit called
“Hertz” or Hz for short.
The number of “Hertz” that a CPU is capable of sustaining is roughly equivalent to the
number of computer instructions the CPU can process per second. More Hertz means
more instructions per second which means a faster CPU.
For example, if you have a 1Hz CPU, that means that the CPU can process roughly one
instruction per second.
CPUs are pretty fast these days, somewhere in the 1,000,000,000 Hz range... that’s a lot
of zeros so to abbreviate computer scientists use the following table:
Hz Good Old Hertz 100 1 Hz
KHz Kilohertz 103 1000 Hz
MHz Megahertz 106 1,000,000 Hz
GHz Gigahertz 109 1,000,000,000 Hz
QUESTION: In 1981 the original IBM PC, ancestor of most modern PCs, had a CPU that
ran at 4.77 MHz. Assuming Moore’s Law has held true, and that the first IBM PC rolled
off the assembly line in January 1981, what should the speed of a modern CPU be today?
QUESTION: Got to Dell’s website and select a desktop computer that would make a
video game nut like me drool with envy. What is the speed of the CPU on this desktop?
How far off is this speed from the one you predicted in the previous question?
QUESTION: The speed for the CPU that you hold in your hand is around 300MHz.
Using the manufacturing date of the computer, and Moore’s Law, what should the speed
of a CPU be today? How far off is this speed from the computer you selected at Dell’s
OK.. now locate the memory card in your computer. The card should be adjacent to two
empty memory slots. Pull the card out and hold it in your hand.
It’s hard to tell how much memory is on the card just by looking at it. Let’s assume the
card has 64 MB of memory. If you are flying through this exercise, you can try looking
up the actual amount by locating the manufacturer and part number someplace on the
card and typing it in to a web search engine like Google.
Here’s a question a friend of mine posed when she was going to buy a computer off the
QUESTION: I want to upgrade the memory of my computer. The computer has three
memory card slots. The first memory slot has two 64 MB of RAM. The second and third
memory slot are empty. I have two options:
- Buy one 512MB memory card for $150.00
- Buy two 256MB memory cards for $60.00 each.
Which option will leave me better off for future memory upgrades?
ANSWER:Pull the hard disk out of the disk drive bay, but don’t disconnect the cables
Disconnect the data cable and trace it with your finger back to the motherboard. Do you
see the second connector?
QUESTION: The first connector connects the hard disk to the data cable and the
motherboard connector connects the data cable to the motherboard. What do you think
the second connector might be used for?
Disconnect the power cable and trace it back to the power supply:
QUESTION: There are a number of power cables that are not connected to anything in
the PC. What do you think these cables are for?
ANSWER: Hold this amazing hard disk in your hand. Look it over carefully. There
should be some
information on a label that indicates how many bytes of memory you can store on the
disk. The information will either be in MEGABYTES or GIGABYTES.
Computer scientists do a lot of strange counting. When computer scientists count how
much memory is in a computer or on a disk they use the following:
byte – a byte can hold a single character, like the letter “A”
KB – kilobyte, 210 bytes
MB – megabyte, 220 bytes
GB – gigabyte, 230 bytes
QUESTION: Locate the size of the hard disk on your hard drive. Convert this size to:
# bytes =
# kilobytes (KB) =
# megabytes (MB) =
# gigabytes (GB) =
QUESTION: Computer scientists also have to estimate things a lot. Estimate the
number of characters that appear on the “Preface” page in your course textbook.
QUESTION: How many bytes is this?
QUESTION: How many copies of your textbook can you store on the hard disk you are
holding in your hand?
ANSWER:Look at the I/O cards. One of these cards is the computer’s network card. This
responsible for getting information to the computer from the network and from the
computer to the network. The card is used whenever someone surfs the web, sends
instant messages, and sends email.
Determine which card is the network card and remove it from the computer. You can
figure out which card is the network card by looking at the back of the computer and
selecting the card which has a receptacle for a network cable. I have a network cable at
the front of the classroom if you want to borrow it.
You are almost done! Put the hardware components you have removed BACK into the
computer, place the cover back on and tighten down the release screws.